added swayam lecture notes

swayam-os-2020/week_01/ipc_files.c

@@ -0,0 +1,39 @@
+/* This program shares file discriptors for Inter Process
+Communictions (IPC) */
+
+#include <stdio.h>
+#include <fcntl.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include <errno.h>
+
+int main(int argc, char const *argv[]) {
+
+  // if file foo.txt does not exist then it is created with permission of 644. Prefix by 0 for octal.
+  int fd = open("foo.txt", O_RDWR | O_CREAT, 0644);
+  if (fd ==-1)
+    // print error code defined in error.h
+    printf("Error Number %d\n", errno);
+
+  printf("File Opened with file descriptor (fd) = %d \n", fd);
+
+  // create copy of the process
+  int pid = fork();
+  if (pid == 0) {
+    sleep(5);   // Wait for Parent to write into the file
+    char buff[100];
+    lseek(fd, 0, SEEK_SET);
+    read(fd, buff, 100);
+    printf("Read from Child. Data = %s\n", buff);
+  } else if(pid > 0) {
+    // The wait() system call suspends execution of the current process until
+    // one of its children terminates.
+    // sleep(5);  // strange behaviour if sleep is put here
+    write(fd, "Hello", 5);
+    wait(0);
+  } else
+    printf("error in fork %d\n", errno);
+
+  return 0;
+}

swayam-os-2020/week_01/pipes_basic.c

@@ -0,0 +1,39 @@
+/* This program creates  a pipe which is a unidirectional data channel that can be used
+   for interprocess communication (IPC). */
+
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <errno.h>
+
+int main(int argc, char const *argv[]) {
+
+  int pipefd[2];
+
+  if (pipe(pipefd) == -1)
+    // print error code defined in error.h
+    printf("Could No create pipe. Error Number %d\n", errno);
+
+    printf("File Opened with file descriptor (pipefd[0] = %d) and pipefd[1] = %d \n",
+      pipefd[0], pipefd[1]);
+
+  // create copy of the process
+  int pid = fork();
+  if (pid == 0) {
+
+    close(pipefd[1]); //close write end of file
+
+    char buff[100];
+    read(pipefd[0], buff, 100);
+    printf("Read from Child = %s\n", buff);
+  } else if(pid > 0) {
+
+    close(pipefd[0]); // close read end of pipe
+    write(pipefd[1], "Hello", 5);
+    wait(0);  // wait for child process to exit
+  } else
+    printf("error in fork %d\n", errno);
+
+  return 0;
+}

swayam-os-2020/week_01/pipes_stdin_stdout.c

@@ -0,0 +1,45 @@
+/* This program creates  a pipe which is a unidirectional data channel that can be used
+   for interprocess communication (IPC). */
+
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <errno.h>
+
+int main(int argc, char const *argv[]) {
+
+  int pipefd[2];
+
+  if (pipe(pipefd) == -1)
+    // print error code defined in error.h
+    printf("Could No create pipe. Error Number %d\n", errno);
+
+    printf("File Opened with file descriptor (pipefd[0] = %d) and pipefd[1] = %d \n",
+      pipefd[0], pipefd[1]);
+
+  // create copy of the process
+  int pid = fork();
+  if (pid == 0) {
+
+    close(pipefd[1]); //close write end of file
+    close(0);  //close standard input
+    dup(pipefd[0]); //Now STDIN and pipfd[0] point to the same data structure
+
+    char buff[100];
+    scanf("%s", buff);
+    //read(pipefd[0], buff, 100);
+    printf("Read from Child = %s \n", buff);
+  } else if(pid > 0) {
+
+    close(pipefd[0]); // close read end of pipe
+    close(1);
+    dup(pipefd[1]);
+    //write(pipefd[1], "Hello", 5);
+    printf("Hello \n");
+    wait(0);
+  } else
+    printf("error in fork %d\n", errno);
+
+  return 0;
+}